Control method of dual-active bridge converter

Abstract

The invention provides a control method of a dual-active bridge converter, and relates to the technical field of power electronics, the method comprises the following steps: firstly collecting output electrical parameters to calculate real-time power, and determining critical power according to a voltage transmission ratio; comparing the real-time power with the critical power, and carrying out segmented optimization control: when the real-time power is not greater than the critical power, solving a phase shift by adopting minimum backflow power optimization control; when the real-time power is greater than the critical power, adopting backflow power and current stress collaborative optimization control, constructing an objective function through weighted summation, and introducing a momentum method to carry out iterative optimization so as to solve an optimal phase shift ratio; and finally, according to the solved phase shift ratio, generating a PWM driving signal to control a switch tube. According to the invention, through a segmented optimization strategy, the backflow power and the current stress are effectively reduced in a wide working condition range, so that the transmission efficiency and the reliability of the converter are improved.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more specifically, to a control method for a dual active bridge converter. Background Technology

[0002] Dual Active Bridge (DAB) converters, as a typical isolated bidirectional DC / DC topology, are widely used in new energy power generation, electric vehicles, and energy storage systems due to their significant advantages in power density, efficiency, reliability, and control flexibility. The performance of a DAB converter largely depends on its modulation method, with common methods including Single-Phase-Shift (SPS), Extended Phase Shift (EPS), and Triple-Phase-Shift (TPS). SPS control adjusts power transmission using only a single phase shift angle, making it simple to implement, but it suffers from high return current power and high current stress, limiting its efficiency. EPS control adds a phase shift angle within the primary bridge to SPS, forming a two-variable collaborative control that significantly improves the system's control flexibility. It not only effectively reduces return current power in the converter but also lowers current stress, thereby improving the overall efficiency of the converter. TPS control, based on EPS, introduces an inner phase shift angle on the secondary side, providing more control degrees of freedom, but increasing control complexity and making it difficult to widely apply in engineering practice.

[0003] Currently, control methods for dual active bridge converters mainly focus on improving converter performance, such as reducing return current power and decreasing current stress. Regarding reducing return current power, common methods include minimum return current power control, which minimizes reactive power cycling by optimizing the phase shift angle, thereby improving efficiency.

[0004] However, these methods typically fail to comprehensively consider the impact of other factors such as current stress and soft-switching conditions on the system, resulting in poor performance over a wide operating range. Regarding reducing current stress, some studies employ optimization algorithms such as the KKT condition method to obtain the global optimal solution for current stress, thereby obtaining the optimal phase shift and effectively reducing the stress on switching devices. However, these methods often neglect the optimization of return power and soft-switching characteristics, potentially leading to decreased system efficiency or reliability issues. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that most existing control methods for dual active bridge converters are optimized for a single performance index and lack consideration for multi-objective collaborative optimization over a wide operating range. In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a control method for dual active bridge converters.

[0006] This invention provides a control method for a dual active bridge converter, comprising the following steps: S1. Acquire the output voltage and output current of the dual active bridge converter, and calculate the real-time output power based on the output voltage and output current. ; S2. Based on the voltage transfer ratio k of the dual active bridge converter, obtain the critical power. ,in ; S3, Real-time output power With critical power Compare; like ≤ Then, minimum return power optimization control is performed. The solution is based on the first objective function with the goal of minimizing return power and the corresponding constraints, to obtain the inward shift ratio D1 and the outward shift ratio D2. like > Then, the return power and current stress co-optimization control is executed. Based on the second objective function containing the weighted sum of return power and current stress and the corresponding constraints, the optimal inward shift ratio D1 and outward shift ratio D2 are obtained by solving through an iterative algorithm. S4. Based on the obtained inner shift ratio D1 and outer shift ratio D2, or the optimal inner shift ratio D1 and outer shift ratio D2, generate the corresponding PWM drive signal, and the controller controls the switching transistors of the dual active bridge converter to perform circuit conversion control.

[0007] Compared with existing technologies, the control method of this application for a dual active bridge converter has the following advantages: below the critical power, return power optimization control is adopted to minimize reactive power loss; above the critical power, return power and current stress collaborative optimization control is adopted. The multi-objective method is transformed into a single-objective function through weighted summation, and the momentum method is introduced to optimize the function, thereby reducing the return power while reducing the current stress, and improving the transmission efficiency and reliability of the converter.

[0008] In one possible implementation, the critical power It is the dual active bridge converter that, under extended phase-shift modulation, can simultaneously satisfy zero return power and the transmission power at the critical point of achieving soft switching; The critical point constraint for zero return current power and soft switching is that the inductor current is zero when the switching transistor undergoes a state change, and its expression is: n is the turns ratio of the transformer in the dual active bridge converter. Let L be the output voltage of the dual active bridge converter, and L be the inductance value of the inductor in the dual active bridge converter. is the switching frequency of the dual active bridge converter.

[0009] Compared with existing technologies, by defining the critical power as the maximum power that satisfies the ideal state of "zero return power and soft switching", and by referencing specific circuit state conditions (inductor current is zero), the abstract mathematical concept is closely linked to the specific circuit operating state, which enhances the rigor and clarity of the technical solution and avoids potential uncertainties.

[0010] In one possible implementation, in step S3, the minimum backflow power optimization control uses the KKT multiplier method to solve for the first objective function; wherein the mathematical expressions for the first objective function and the constraints are: in, For the optimal solution set, This is the per-unit value of the converter's return power. This refers to the actual transmission power. For the desired transmission power, This is a soft-switching constraint. For KKT operators.

[0011] Compared with existing technologies, by introducing specific optimization mathematical methods, the solution is transformed into a concrete and feasible technical means, which reflects the advanced nature and feasibility of the solution and provides a foundation for further limiting the optimal solution.

[0012] In one possible implementation, when 0 ≤ D2 ≤ D1 ≤ 1, the optimal solution for the inward shift ratio D1 and the outward shift ratio D2 is: Where P represents the real-time transmission power.

[0013] Compared with existing technologies, this method provides an analytical solution for the optimal shift ratio under specific constraints, which eliminates the need for complex online iterative calculations in the low-power region, greatly reducing the computational burden and improving real-time control efficiency.

[0014] In one possible implementation, in step S3, the second objective function H in the coordinated optimization control of return power and current stress is: in, This represents the per-unit current stress. This represents the normalized return power. is the weighting coefficient for current stress, and .

[0015] Compared with existing technologies, the weighted summation method transforms the two contradictory objectives of "reducing current stress" and "reducing return power" into a solvable single-objective optimization problem, thus protecting the core concept of collaborative optimization in the high-power region.

[0016] In one possible implementation, the per-unit current stress The calculation formula is: Per-unit return power The calculation formula is: .

[0017] Compared with existing technologies, this paper further defines the specific per-unit calculation formulas for two key performance parameters (current stress and return power) in the weighted summation method, making the abstract objective function concrete and calculable, and ensuring the clarity and feasibility of the technical solution.

[0018] In one possible implementation, the constraints corresponding to the second objective function H include: Transmission power equality constraint: Compared to constraints: Current stress weight constraint: Power region constraints: .

[0019] Compared with existing technologies, this approach forms a rigorous multivariate constraint system by encompassing power balance, the physical range of the shift ratio, the range of weighting coefficients, and power region discrimination. This system fully defines all constraints of the optimization problem in the high-power region, ensuring that the optimization results are physically feasible and superior in performance, thus demonstrating the completeness and robustness of the solution.

[0020] In one possible implementation, the momentum method is used to iteratively optimize the second objective function H; the iterative process of the momentum method includes: Calculate the momentum variable at the current iteration time: ; Update optimization parameters based on momentum variable: ; in, The momentum at the current moment; The momentum of the previous moment; Momentum factor The learning rate; This is the gradient of the current parameters.

[0021] Compared with the gradient descent method in existing technologies, introducing the momentum method, a specific optimization algorithm, to solve complex nonlinear optimization problems can accelerate convergence and prevent getting trapped in local optima, directly improving the efficiency of optimization and the quality of the global optimal solution.

[0022] In one possible implementation, the termination condition of the iterative process is: Define iterative difference ; When the iteration difference Less than or equal to the preset iterative reference difference If the number of iterations exceeds the preset maximum number of iterations, stop the iteration and output the current parameters as the optimal solution.

[0023] Compared with existing technologies, by defining two criteria, iteration difference and maximum number of iterations, the control algorithm can ensure that it can output stable and reliable results within a finite time, balancing control accuracy and real-time performance, and avoiding infinite loops or premature termination. Attached Figure Description

[0024] Figure 1 This is a topology diagram of the dual active bridge converter of the present invention; Figure 2 For the present invention Figure 1 Waveform diagram illustrating the working principle of a dual active bridge converter under EPF modulation; Figure 3 This is a two-dimensional curve of the transmission power of the dual active bridge converter under zero return power and soft switching conditions according to the present invention; Figure 4 This is a flowchart of the control method for the dual active bridge converter of the present invention. Detailed Implementation

[0025] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of this application and are not intended to limit the scope of protection of the embodiments of this application. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0026] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0027] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0028] See Figure 1 The diagram shown is a topology of the dual active bridge converter of this application, which is prior art. See also... Figure 2 As shown, Figure 1 The waveform diagram illustrating the working principle of the dual active bridge converter under EPF modulation. Figure 2 In the vertical coordinate system, P1, P2, P3, P4, S1, S2, S3, and S4 represent respectively... Figure 1 The corresponding drive waveform of the switching transistor in the middle; Figure 2 Uab in the vertical axis is Figure 1 Voltage waveforms at points ab in the middle; Figure 2 Ucd in the vertical axis is Figure 1 Voltage waveforms at points c and d in the middle; Figure 2 In the vertical axis, iL is Figure 1 The waveform of the current flowing through inductor L1.

[0029] See Figure 4 As shown, this application discloses a method based on Figure 1 and Figure 2 The control method for the dual active bridge converter shown includes the following steps: S1. Acquire the output voltage and output current of the dual active bridge converter, and calculate the real-time output power based on the output voltage and output current. ; S2. Based on the voltage transfer ratio k of the dual active bridge converter, obtain the critical power. ,in ; S3, Real-time output power With critical power Compare; like ≤ Then, minimum return power optimization control is performed. The solution is based on the first objective function with the goal of minimizing return power and the corresponding constraints, to obtain the inward shift ratio D1 and the outward shift ratio D2. like > Then, the return power and current stress co-optimization control is executed. Based on the second objective function containing the weighted sum of return power and current stress and the corresponding constraints, the optimal inward shift ratio D1 and outward shift ratio D2 are obtained by solving through an iterative algorithm. S4. Based on the obtained inner shift ratio D1 and outer shift ratio D2, or the optimal inner shift ratio D1 and outer shift ratio D2, generate the corresponding PWM drive signal, and the controller controls the switching transistors of the dual active bridge converter to perform circuit conversion control.

[0030] Below the critical power, return power optimization control is adopted to minimize reactive power loss; above the critical power, return power and current stress co-optimization control is adopted. The multi-objective method is transformed into a single objective function by weighted summation, and the momentum method is introduced to optimize the function. This reduces the return power while reducing the current stress, thereby improving the transmission efficiency and reliability of the converter.

[0031] In step S2, the critical power The specific definition is as follows.

[0032] See Figure 2 As shown, to achieve zero return power in a dual active bridge converter under EPS modulation, the constraint condition is as follows: ,exist To achieve soft-switching characteristics at all times, the following constraints apply: Therefore, the constraints for achieving zero return power and soft-switching characteristics in a dual active bridge converter are: .

[0033] Right now: (1.1) Compared to the inward shift of the original side H-bridge; Compared to the outward shift of the H-bridges on both sides; n is the turns ratio of the transformer in the dual active bridge converter; is the output voltage of the dual active bridge converter; L is the inductance value of the inductor in the dual active bridge converter; is the switching frequency of the dual active bridge converter.

[0034] Further simplification: (1.2) Simplifying the analysis, by substituting K=1 into the transmission power expression for EPS modulation, we can obtain the transmission power that satisfies the zero return power and soft-switching constraints. : (1.3) See Figure 3 As shown, the area enclosed by the two red curves represents the power transmission range under EPS modulation, while the blue curve represents the area under EPS modulation. The curve represents the power transmission curve of the dual active bridge converter under the conditions of zero return power and soft switching.

[0035] Operating Condition 1: When The dual active bridge converter satisfies the constraints of soft switching and zero return power. The dual active bridge converter is located in power region 2, meaning its power range is as follows: (1.4) Operating Condition 2: When The dual active bridge converter does not meet the constraints of soft switching and zero return power. The power region 1 of the dual active bridge converter, that is, the power range in which the dual active bridge converter is located, is: (1.5) Therefore, the critical power can be defined as follows: (1.6) Below the critical power level, the system is in power region 2, where zero return current and soft switching can be achieved simultaneously. Above the critical power level, the system is in power region 1, where zero return current and soft switching cannot be achieved simultaneously.

[0036] In step S3, ≤ The minimum return power optimization control is performed, and the specific steps are as follows.

[0037] Considering the effects of transmission power and soft switching, the KKT multiplier method is used, with return current power as the objective constraint, transmission power as an equality constraint, and soft switching as an inequality constraint, to minimize the return current. Its mathematical expression is: (2.1) in, For the optimal solution set, This is the per-unit value of the converter's return power. This refers to the actual transmission power. For the desired transmission power, This is a soft-switching constraint. For KKT operators.

[0038] Further expansion of the established Lagrange function polynomial is as follows: (And when 0≤D2≤D1≤1, the transmission power of the DPS is below the critical power.) L= + (2.2) The optimal solution within this range is: (2.3) At this point, the minimum return power is: (2.4) In step S3, > The specific steps for implementing coordinated optimization control of return power and current stress are as follows.

[0039] To simultaneously achieve the two optimization objectives of reducing return current power and current stress, a weighted summation method for multi-objective optimization is adopted, defining the weight of current stress as follows: The weight of the return power is 1- .

[0040] Construct the objective function for weight optimization: (3.1) in, For current stress, This is the recirculation power.

[0041] When the dual active bridge converter operates under EPS control, by Figure 2 Know Maximum current occurs at all times, current stress expression: (3.2) Take the maximum value as the baseline: ; Per-unit current stress : (3.3) Return power expression: (3.4) The maximum value is the baseline value: ; Per-unit return power : (3.5) Constraints: The transmission power equality constraint, the shift ratio constraint, the current stress weight constraint, and the power region constraint are respectively ; .

[0042] Based on the above analysis, the problem of co-optimizing current stress and return power in a dual active bridge converter can be expressed as: (3.6) In optimization problems using the weighting method, determining the weight values ​​is crucial. For the established objective function, the momentum method is used to optimize the objective function, defining a momentum variable. To accumulate information about historical gradients, its expression is: (3.7) in, It is the momentum at the current moment; It is the momentum from the previous moment; It is the momentum factor (usually set to 0.9), which controls the weight of historical gradients; It is the learning rate; It is the gradient of the current parameters.

[0043] (3.8) The iterative equation for optimizing the parameters of the objective function H is as follows: (3.9) Define the iterative difference: (3.10) By setting the iterative reference difference With the maximum number of iterations, when The iteration ends when the number of iterations exceeds the maximum number of iterations, thus obtaining the optimal control solution.

[0044] To improve the transmission efficiency and reduce switching stress of the dual active bridge converter over a wide operating range, this embodiment proposes a segmented optimization control strategy based on EPS modulation: below the critical power, return current power optimization control is used; above the critical power, return current power and current stress collaborative optimization control are used. The collaborative optimization control employs a weighted summation method, and a momentum method is proposed to optimize the selected objective function, which is beneficial for further optimizing current stress and reducing return current power.

[0045] This embodiment has the following beneficial effects: Improve the converter's transmission efficiency by optimizing transmission efficiency under a wide range of operating conditions; Reduce the stress on the converter switching transistors and lower the selection cost.

[0046] In the description of the embodiments of this application, it should be noted that the terms "inner" and "outer" and other terms indicating direction or positional relationship are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or component must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this application.

[0047] In the description of this application, the references to terms such as "an embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0048] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A control method of a dual active bridge converter, characterized by, The method comprises the following steps: S1, collect the output voltage and output current of the dual active bridge converter, and calculate the real-time output power based on the output voltage and output current ; S2, according to the voltage transfer ratio k of the dual active bridge converter, get the critical power wherein ; S3, compare the real-time output power with the critical power ; If ≤ , the minimum backflow power optimization control is performed, and the inner shift phase ratio D1 and the outer shift phase ratio D2 are obtained based on the first objective function and the corresponding constraint condition for minimizing the backflow power. If > then the reflow power and current stress co-optimization control is performed, based on a second objective function including the reflow power and current stress weighted sum and corresponding constraint conditions, the optimal inner shift ratio D1 and outer shift ratio D2 are obtained by solving through an iterative algorithm. S4. According to the obtained internal phase shift ratio D1 and external phase shift ratio D2, or the optimal internal phase shift ratio D1 and external phase shift ratio D2, a corresponding PWM driving signal is generated, and a controller controls the switching tube of the dual active bridge converter to perform circuit conversion control.

2. The control method of a dual active bridge converter according to claim 1, characterized in that, Critical power The critical point of transmission power of a dual active bridge converter under extended phase-shift modulation, which can simultaneously meet zero backflow power and soft switching. The critical point constraint condition of the zero reflux power and the soft switch is that the current of the inductor is zero when the state of the switching tube changes, and the expression is: n is the turns ratio of the transformer in the dual active bridge converter, Vout is the output voltage of the dual active bridge converter, L is the inductance value of the inductor in the dual active bridge converter, f is the switching frequency of the dual active bridge converter.

3. The control method of a dual active bridge converter according to claim 1, characterized in that, In step S3, in the minimum backflow power optimization control, the KKT multiplier method is used to solve the first objective function ; The first objective function is The mathematical expression of the constraint condition is: wherein, is the optimal solution set, is the unit of the converter backflow power, is the actual transmission power, is the expected transmission power, is the soft switching constraint condition; is the KKT operator.

4. The control method of the dual active bridge converter according to claim 3, characterized in that, When 0≤D2≤D1≤1 is satisfied, the optimal solution of the internal phase shift ratio D1 and the external phase shift ratio D2 is: Wherein, P is the real-time transmission power.

5. The control method of a dual active bridge converter according to claim 1, characterized in that, In step S3, in the reflux power and current stress collaborative optimization control, the second objective function H is: wherein, is the current stress normalized, is the reflow power normalized, is the weight coefficient of the current stress, and .

6. The control method of the dual active bridge converter according to claim 5, characterized in that, The current stress after normalization The calculation formula is: The normalized backflow power The calculation formula is: 。 7. The control method of a dual active bridge converter according to claim 5, characterized in that, The constraint condition corresponding to the second objective function H includes: Transmission power equation constraint: Phase shift ratio constraint: Current stress weight constraint: Power region constraint: .

8. The control method of a dual active bridge converter according to any one of claims 5 to 7, characterized in that, The momentum method is used for iterative optimization of the second objective function H; The iterative process of the momentum method includes: Compute the momentum variable at the current iteration time instant: ; Updating the optimization parameters according to the momentum variable: ; where, is the momentum at the current time step; is the momentum at the previous time step; is the momentum factor, is the learning rate; is the gradient of the current parameter.

9. The control method of a dual active bridge converter according to claim 8, characterized in that, The termination condition of the iterative process is: Define the iterative difference: ; When the iteration difference is less than or equal to a preset iteration reference difference , or the iteration number is greater than a preset maximum iteration number, stop iteration and output the current parameter as the optimal solution.

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